1. Field of the Invention
The invention relates to an image display apparatus that displays image information due to a change in the optical properties thereof caused by an applied electric field.
2. Description of the Related Art
Various display modes for image display apparatuses known as electronic papers are known. Examples of the display modes proposed for image display apparatuses include a microcapsular electrophoretic display displaying an image by electrophoretic movement of positively charged white particles and negatively charged black particles, a cholesteric-liquid-crystal selective-reflection display displaying an image by selective reflection by a cholesteric liquid crystal formed with a chiral agent and a nematic liquid crystal, and the like.
The modes of applying voltage to a display layer having optical properties that change in response to an electric field, in the image display apparatuses include, for example, a passive mode of applying voltage by using a single matrix electrode, and an active mode of applying voltage by using a field-effect transistor. The active drive mode is characteristically faster in display velocity, higher in definition of the display image, and superior in reproducing a halftone image than the passive mode.
The field-effect transistor used in the active drive mode includes a gate insulator and a semiconductive layer, and amorphous silicon or polysilicon has been used as the semiconductive layer. However, recently, use of an organic compound has been proposed for the semiconductive layer. Use of an organic compound is expected to be effective in improving properties such as flexibility of the field-effect transistor and the productivity thereof in the coating method, compared to use of an inorganic compound. Examples of the films of organic conjugated polymer that have been used as the semiconductive layer in the field-effect transistor include π-conjugated polymer thin films prepared by electrolytic polymerization (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 62-85467), films prepared by coating a solution of a π-conjugated polymer or the precursor thereof (see, for example, JP-A No. 5-110069), and the like.
The organic compounds have a problem of low durability, when used as the semiconductive layer. A method of adding an ultraviolet absorber to the organic semiconductive layer has been proposed for improvement in the durability (see, for example, JP-A No. 2005-5582), but remains unsatisfactory.
Further, as for a fluorescent brightener absorbing light at 410 nm or less at an absorbance of 90%, use of benzoxazole derivatives as a coating has been disclosed (see, for example, JP-A No. 2002-80788).